Blind dating - mate finding in planktonic copepods. III. Hydromechanical communication in Acartia tonsa

Mate-finding behaviour in the marine copepod Acartia tonsa was examined by video analysis. A. tonsa appears to depend on hydromechanical signals in the location of mates, detected at distances of up to 5 or 7 mm. Series of up to 7 or 8 synchronised hops in closely situated individuals, interpreted as an expression of hydromechanical communication or assessment of a potential partner, often concluded with mating. We use previously published models of hydrodynamic signalling to explain the observed behaviour and extrapolate the results to other species

Effect of the toxic dinoglagellate Alexandrium minutum on the copepod Euterpina acutifrons

4 pages, 3 figures, 1 table.-- Proceedings of the Seventh International Conference on Toxic Phytoplankton, Sendai (Japan), 12-16 July 1995The effects of Alexandrium minutum strains with differing toxin contents on the pelagic harpacticoid copepod Euterpina actifrons were studied. In small volume experiments (350 ml), both strins strongly reduced naupliar activity (defined as movement) to 70% of the individuals after 24h of exposure. A considerable proportion of the copepodites and adult females (`producing viable eggs) survived all five days of the experiment. Inactivation of nauplii was also observed in medium volume experiments (6 l), reaching 50% after 3 days of exposure to the more toxin strain. In large volume experiments (20 l), 10-15% of females were inactive after 1-2 days of exposure to concentrations of 103 cells ml-1 of both strains and of 104 cells ml-1 of the most toxic strain. The very low values of animal toxicity obtained by HPLC analysis of the copepods indicate that Euterpina did not feed actively on the algae. The cell-free filtrate from A. minutum (most toxic strain) cultures also had a deleterious effect on nauplii. It is suggested taht E, acutifrons avoids grazing the toxic algae after ingesting a few cells, but that the dinoflgellates may exude toxins or other substances affecting the copepodsThis study was supported with funds from projects 11.02 of the Instituto Español de Oceanografía and ALI 92-0111-C02-01 of CICYTN

Effects of two paralytic shellfish toxin producing dinoflagellates on the harpacticoid copepod Euterpina acutifrons

The effects of two paralytic shellfish toxin (PST) producing dinoflagellates, Alexandrium minutum Halim (high and low toxin strains) and Gymnodinium catenatum Graham, on the pelagic harpacticoid copepod Euterpina acutifrons Dana were tested in a series of experiments run from October 1994 to May 1995. In small volumes (350 ml), both strains of A. minutum (300 to 350 cells ml-1), and G. catenatum (175 cells ml-1), strongly reduced naupliar activity (about 30 and 17% were inactive after 24 h, respectively). Activity is here defined as movement. In medium volumes (6 litre), 40% of nauplii incubated with the high toxin strain of A. minutum (1000 cells ml-1) and 8% of nauplii incubated with cell-free filtrate of the same culture were inactive after 24 h; these values increased to 50 and 30% respectively after 3 d. In large volumes (20 litre), adult copepods incubated with A. minutum (1000 and 10000 cells ml-1) for 5 d revealed only trace levels of PSP-toxins (paralytic shellfish poisoning) in the extracts analysed by HPLC. With both strains of A. minutum (1000 and 10000 cells ml-1), 10 to 15% of the copepods were inactive after 1 to 2 d. It is suggested that E. acutifrons avoids feeding on the dinoflagellates after tasting a few cells, but that the dinoflagellates may exude toxins or other substances that affect the copepods. The inactivating effect of the toxic dinoflagellates on the nauplii was more rapid and stronger than on adult copepods, although strong inactivation and death were also observed in adults with time (up to 80% were inactive after 5 d of incubation with A. minutum). Still, in our experiments a considerable proportion of adult females incubated with the toxic dinoflagellates remained active and were able to produce viable eggs for several daysPublicado

Long term effects of self-determination theory and motivational interviewing in a web-based physical activity intervention: randomized controlled trial

Background: Our main objective in the current study was to evaluate the long-term effectiveness (12 months from baseline) of I Move (a web-based computer tailored physical activity intervention, based on self-determination theory and motivational interviewing). To this end, we compared I Move to a web-based computer tailored physical activity intervention based on traditional health behavior theories (Active Plus), and to a no-intervention control group. As a secondary objective, the present study aimed to identify participant characteristics that moderate the long term effects of I Move and Active Plus. Methods: A randomized controlled trial was conducted, comparing three research conditions: 1) the I Move condition, participants in this condition received I Move; 2) the Active Plus condition, participants in this condition received Active Plus; 3) the control condition; participants in this condition received no intervention and were placed on a waiting list. Main outcome measures were weekly minutes of moderate to vigorous physical activity and weekly days with minimal 30 min of physical activity. All measurements were taken by web-based questionnaires via the study website. Intervention effects were analyzed using multilevel linear regression analyses. Results: At 12 months from baseline, I Move was found to be effective in increasing weekly minutes of moderate to vigorous physical activity (ES = .13), while Active Plus was not. In contrast, Active Plus was found to be effective in increasing weekly days with >= 30 min PA at 12 months (ES = .11), while I Move was not. No moderators of the effects of I Move were found. Conclusions: The results suggest that web-based computer tailored physical activity interventions might best include elements based on both self-determination theory/motivational interviewing and traditional health behavioral theories. To be more precise, it is arguable that the focus of the theoretical foundations, used in new web-based PA interventions should depend on the intended program outcome. In order to draw firm conclusions, however, more research on the effects of self-determination theory and motivational interviewing in web-based physical activity promotion is needed